The invention relates to the general field of read-write heads for magnetic disk systems with particular reference to reducing the lengths of tracks recorded using stitched heads.
An example of a read-write head for a magnetic disk system is schematically illustrated in FIG. 1. The magnetic field that xe2x80x98writesxe2x80x99 a bit at the surface of recording medium 15 is generated by a flat coil whose windings 14 can be seen in the figure. The magnetic flux generated by the flat coil is concentrated within upper and lower pole pieces 12 and 13 respectively which, while being connected at a point on the extreme left of the figure, are separated by small gap 16. Thus, most of the magnetic flux generated by the flat coil passes across this gap with fringing fields extending out for a short distance where the field is still powerful enough to magnetize a small portion of recoding medium 15. The distance between pole pieces 12 and 13 and writeable surface 15 is typically between about 10 and 50 nm.
In practice, lower pole 13 is also used as a magnetic shield for the reading assembly that is located immediately adjacent to it, being therefore referred to as a shared magnetic layer. The rest of the head is shown in FIG. 2 and is made up of reading element 21 and a second shield 22. The reading element 21 is itself a composite of many layers. Also detailed in FIG. 2 is the structure of upper pole 12 near the gap 16. Seen there is sub-pole 23 whose area (at the gap) is significantly less than that of the opposing flat portions of 12 and 13 that make up the gap region 16 in FIG. 1. The introduction of this sub-pole serves to further concentrate the magnetic flux across gap 16 making for more intense fringing fields in its vicinity. A more detailed view of the sub-pole assembly is shown in FIG. 3. As can be seen, sub-pole 23 is separately formed relative to upper pole 12 and so the full structure is sometimes referred to as a xe2x80x98stitchedxe2x80x99 head. Layer 16 defines the write gap and can be a metal or an insulator. The remaining space 35 is filled with an insulating material.
The principle governing the operation of read sensor 21 is the change of resistivity of certain materials in the presence of a magnetic field (magneto-resistance). In particular, most magnetic materials exhibit anisotropic behavior in that they have a preferred direction along which they are most easily magnetized (known as the easy axis). The magneto-resistance effect manifests itself as an increase in resistivity when the material is magnetized in a direction perpendicular to the easy axis, said increase being reduced to zero when magnetization is along the easy axis. Thus, any magnetic field that changes the direction of magnetization in a magneto-resistive material can be detected as a change in resistance.
The magneto-resistance effect can be significantly increased by means of a structure known as a spin valve. The resulting increase (known as Giant magneto-resistance or GMR) derives from the fact that electrons in a magnetized solid are subject to significantly less scattering by the lattice when their own magnetization vectors (due to spin) are parallel (as opposed to anti-parallel) to the direction of magnetization of the solid as a whole.
The improvements provided by GMR devices, in the density of magnetic data that can be read, are of little value if there is no corresponding increase in the density of magnetic data that can be written. Thus there is a need for ultrahigh density recording heads with sub-poles having sub-micron widths. As we will detail below, formation of sub-pole 23 involves the use of exceptionally thick layers of photoresist (up to 7 microns) while at the same time keeping the width of sub-pole 23 even narrower than 0.5 microns with vertical side-walls. This is very difficult for conventional photoresist processes. The width in question is marked as W in FIG. 4 which is an isometric representation of FIG. 3. Note that the front surface 523 of the structure seen in FIG. 4 is part of a plane, known as the air bearing surface (ABS), that flies past recording surface 15 (of FIG. 3).
The present invention is therefore directed towards a method for manufacturing the three dimensional object 423 of FIG. 4 whose front surface is shown there as 523. It has been found that several problems arise once width W goes below about 0.5 microns. The present invention shows how these problems may be overcome.
A routine search of the prior art was performed but no references that teach the exact processes and structures of the present invention were discovered. Several references of interest were, however, encountered along the way. For example, Pinarbasi in U.S. Pat. No. 5,883,764 uses PMGI in a liftoff process while forming a GMR element. In U.S. Pat. No. 5,491,600 Chen et al. teach a similar approach to that later adopted by Pinarbasi while, in U.S. Pat. No. 5,649,351, Cole et al. teach how to form a doubly stitched sub-pole.
It has been an object of the present invention to provide a process for manufacturing a narrow track stitched head for ultrahigh density magnetic recording applications.
A further object of the invention has been that said write head take full advantage of the densities that can be read with advanced GMR heads.
Another object of the invention has been to provide a process for forming a mold, in photoresist, having narrow width and high aspect ratio.
Still another object of the invention has been to fill said narrow mold with metal that is free of flaws and irregularities.
These objects have been achieved by introducing a layer of PMGI (poly-dimethylglutarimide) between the planarized positive photoresist layer that comprises the mold and the non-magnetic write gap layer on which the mold rests. This greatly facilitates formation of a high aspect ratio hole with a clean flat bottom and essentially vertical sides as well as the subsequent removal of the photoresist after said hole has been filled through electroplating to form a stitched sub-pole.